This application is based upon and claims benefit of priority of Japanese Patent Applications No. Hei-11-305817 filed on Oct. 27, 1999 and No. 2000-72497 filed on Mar. 10, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an instrument panel having a pointer driven by a motor for use in an automobile vehicle or other devices.
2. Description of Related Art
An example of this kind of instrument panel is disclosed in JP-A-9-21655. In the instrument panel disclosed therein, a device for driving a pointer is installed behind a printed circuit board and electrically connected to the circuit board by soldering. Another example is shown in JPA-8-233611. The instrument panel shown therein includes a stepping motor for driving a pointer via a reduction gear train. Gears constituting the reduction gear train are made of synthetic resin to suppress gear noises and to reduce the weight.
The gears made of synthetic resin, however, are weak against the heat that is generated in a soldering process such as flow-soldering or reflow-soldering. The gears tend to be damaged by the heat in the soldering-process.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved instrument panel which is easily manufactured without causing damages on heat-sensitive components by the soldering heat.
An instrument panel such as a combination meter for use in an automotive vehicle includes one or more pointers driven by a motor such as a stepping motor. The instrument panel is composed of a front panel having scales and numerals printed thereon, a rotatable pointer, a stepping motor for driving the pointer, a reduction gear train disposed between the pointer and the motor to reduce the rotational angle of the motor, and a circuit board for electrically connecting a field coil of the motor and other components. The circuit board is positioned behind the front panel forming a certain space therebetween. The reduction gear train includes plural gears made of synthetic resin which is weak and sensitive to heat. Terminals of the field coil are soldered on the circuit board under a reflow-soldering or flow-soldering process.
To protect the heat-sensitive resin gears from heat of soldering, components such as the field coil are first supported on the circuit board and soldered thereon. After cooling down the heat of soldering, the reduction gear train having heat-sensitive resin gears is mounted on the circuit board. A stator of the motor having the field coil may be placed at the front side of the circuit board, and a rotor of the motor and the reduction gear train may be placed at the rear side. An entire motor including its rotor may be placed at the front side of the circuit board, and only the reduction gear train may be placed at the rear side.
Alternatively, an entire driver device including the motor and the reduction gear train may be positioned at the rear side of the circuit board, as long as the field coil is soldered on the circuit board first and then the reduction gear train is mounted on the circuit board after the soldering heat is dissipated. In this structure, a wide space is available at the front side of the circuit board. Accordingly, other components such as an illuminating light source are easily disposed at the front side.
A light-conductive plate having a cutout opening may be attached to the rear surface of the front panel. In this case, the components such as the stator placed at the front side of the circuit board can be positioned in the cutout opening to reduce the thickness of the instrument panel.
The heat-sensitive resin gears are protected against the soldering heat according to the present invention. Further, an automatic reflow- or flow-soldering process can be used to reduce the manufacturing cost.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.